Studies are in progress to understand the mechanism of blocking factor from intraperitoneal fluid of Balb/C mice having methyl cholanthrene-induced fibrosarcoma. Different techniques of immunoabsorption have been employed to identify different subclasses of immunoglobulin and their blocking activity. Column chromatography is being used to isolate and further purify the blocking factor. Tumor cells grown in vitro will be used to absorb out the blocking factor from intraperitoneal fluid. After repeated absorption, it shall be evaluated to determine if the blocking activity of the intraperitoneal fluid is lost. The coated tumor cells will be used for eluting the blocking factor from the tumor cell membrane surface. Spleen from tumor-induced mice is being studied for the T and B cells. Increase of B cells in spleen may be having the inhibiting effect on the cytotoxic T cells and, hence, on the tumor growth. In vitro culture of B cells shall be used to determine whether antibody released by their cells has a blocking effect.